1. Field of the Invention
The present invention relates to a form measuring apparatus and a form measuring method which pertain to a pattern projection type based on a phase shifting technique.
2. Description of the Related Art
As a technique of measuring surface form of a measuring object (three-dimensional form) in a non-contact manner, there have been known three-dimensional form measuring apparatuses of a pattern projection type based on a phase shifting technique. Such a three-dimensional form measuring apparatus projects a fringe pattern having a sinusoidal intensity distribution onto a measuring object, and repeatedly takes an image of the measuring object while shifting the phase of the fringe pattern at a constant pitch. A phase distribution (phase image) of the fringe deformed according to the surface form of the measuring object is found or obtained by applying a plurality of images (brightness variation data) obtained in the above manner to a predetermined computational expression. Then the phase image is converted into a height distribution (height image) of the measuring object after unwrapping the phase image (phase unwrapping).
Incidentally, the three-dimensional shape measuring apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-214653 acquires the brightness variation data under two capturing conditions different in projection light amount, evaluates the contrast values of two different brightness variation data according to each pixel, and excludes the brightness variation data with the lower contrast value from the computing objects in order to prevent measurement error due to saturated pixels.